The present invention relates to a system for controlling the frequency of an audio signal to be reproduced by an audio device such as a tape deck.
It is preferable that the audio device, such as the receiver, tape player, and CD player, has a flat frequency characteristic. In order to obtain the flat frequency characteristic, various compensation methods are used in the audio system. However, the magnetic tape has not inherently the flat reproduction characteristic. Namely, an audio signal in a high frequency range recorded on the magnetic tape can not be sufficiently reproduced, in general. As a result, the reproduced music sound has often dull tone.
Meanwhile, it is known that stimuli having the l/f fluctuation offer one comfort (U.S. Pat. No. 4,338,945). Namely, pleasant stimuli such as the frequency fluctuation of good music has the l/f fluctuation. Here, the l/f fluctuation is that the power-density spectrum of the quantity which fluctuates with time (.vertline.F(j.omega.).vertline..sup.2 where F(j.omega.) is Fourier transform of the quantity) is a fluctuation having the frequency distribution of l/.omega. (.omega.=2.pi.f).
FIG. 1 shows reproduction characteristics of a CD and a magnetic tape on which a music is recorded, respectively. As is understood from the graph, the CD has a reproduction characteristic approximates to the l/f fluctuation. However, the characteristic of the magnetic tape fairly deviates from the l/f fluctuation.
If the recorded music on the magnetic tape is reproduced along the l/f characteristic, the listener will feel at ease with the reproduced music.